Levelling a bathroom floor

We had a loft extension built late last year but couldn't afford to get the bathroom done at the time.

I've just spent the last few weekends getting the pipework in the right place and fitted the shower base.

The subfloor is 18mm plywood and it's supported by joists at 370-420mm centres. Having screwed the plywood down I've discovered that the new joists aren't level. They are all level to themselves but a few of them are lower compared to their neighbours. I've got an 8mm dip in the middle of the room.

I'm thinking of using a flexible self levelling compound (Mapei) and had a few questions.

I'm planning to overboard with 6mm ply, should I level before putting this down or after?

Should I level the whole floor or install the bath first and level around that?

I'm using a click LVT on top of it all.

 

Make sure you seal all gaps before you screed over it bit yes I'd 6mm ply it and feather all joints/edges then flow some renovation over it.

Do the prep when it's empty and fit the click after you have put the bath tub etc in.

 

If it's easy enough to lift the ply again, you could always just put a straight edge across the joists and build up the height of the lower joists with strips of ply or something, then re lay the ply

 

I can't lift the ply now - there's a shower tray mortared on to it that I'd need to smash off. A lesson learned in not assuming that the builders have put everything level.

 

Could level up and ply over or ply first then level. I would defo fit it before all the stuff goes in but clic shouldn’t be pinned down. Stick down would be better


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I was reading something that said not to level before the top ply because when screwing the top ply down the screed would break up where the screws went through?

I was planning to fit the bath to the subfloor and build a frame for it then level the rest of the room using the frame to stop the screed running under. I wasn't going to floor under it because of needing to screw the bath frame/feet down. I'm flooring under the basin and toilet. Should I be doing under the bath as well?

 

You having a bath panel then I take it?
Not a freestanding bath tub?

 

Yes, J shaped bath with a panel

 

If you are batterning for the panel to sit against then you can put your bath in before the prep then.